1. Technical Field
The present invention is directed to the field of electronic filters. More particularly, the present invention provides a compact waveguide filter exhibiting high-pass, band-pass and low-pass response from a single filter structure, which is capable of handling high-powered microwave signals in the GHz frequency range.
2. Description of the Related Art
Waveguide filters are known in this art. There are two primary types of filters for use in the microwave frequency range (i.e. from about 2-15 GHz), symmetrically corrugated filters and iris filters. However, both of these types of filters suffer from many disadvantages.
An example of a symmetrically corrugated filter is shown in U.S. Pat. No. 3,597,710 to Levy ("the '720 patent). FIG. 1 of the '720 patent shows a standard E-plane corrugated structure having a uniform waveguide channel with a plurality of symmetrical corrugations. But as noted in the '720 patent, these types of corrugated filters are typically low-pass only. Such a filter typically cannot provide a band-pass response.
The '720 patent purports to have advantages over the standard corrugated structure by forming a plurality of capacitive irises. Instead of forming a uniform waveguide channel, the '720 patent provides a series of iris structures (FIGS. 2 and 6), which have different heights. Although the irises and the corrugations are of different height, for any one iris or corrugation, the structure is symmetrical. Another example of an iris filter (known as an H-plane iris filter) is shown in U.S. Pat. No. 2,585,563 to Lewis, et al. These types of iris filters suffer from many disadvantages, however. First, they typically provide band-pass response only, i.e., they are incapable of providing a combination response, such as low-pass and band-pass. Secondly, the iris filter is typically a large structure, as the irises are generally separated along the waveguide channel by a half of a wavelength (.lambda.g/2). Since the number of irises typically correlates to the order of the filter, this results in a very large filter when the order of the filter is high, such as 5th order or greater.
Other types of filters include resonant iris filters (as shown in U.S. Pat. Nos. 1,788,538 to Norton and 1,849,659 to Bennett) and evanescent-mode ridged filters (as shown in U.S. Pat. No. 4,646,039 to Saad). The resonant iris filter utilizes a plurality of resonant diaphragms as resonating elements that are separated by a quarter of a wavelength (.lambda.g/4). The evanescent-mode ridged filter is based on a wavelength structure with a ridged cross section. However, a common problem with both of these types of filters is that they typically cannot handle high-powered signals.
Therefore, there remains a general need in this field for a compact waveguide filter that provides a combination response and is capable of handling high-powered signals in the GHz range.